drm/i915/selftests: Add the mock engine to the gt->engine[]

Remember to include the newly created mock engine in the list of
available engines inside the gt.

Fixes: a50134b1 ("drm/i915: Make for_each_engine_masked work on intel_gt")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191018130703.31125-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/mock_engine.c

@@ -253,6 +253,7 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
 	snprintf(engine->base.name, sizeof(engine->base.name), "%s", name);
 	engine->base.id = id;
 	engine->base.mask = BIT(id);
+	engine->base.legacy_idx = INVALID_ENGINE;
 	engine->base.instance = id;
 	engine->base.status_page.addr = (void *)(engine + 1);
 
@@ -267,6 +268,9 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
 	engine->base.reset.finish = mock_reset_finish;
 	engine->base.cancel_requests = mock_cancel_requests;
 
+	i915->gt.engine[id] = &engine->base;
+	i915->gt.engine_class[0][id] = &engine->base;
+
 	/* fake hw queue */
 	spin_lock_init(&engine->hw_lock);
 	timer_setup(&engine->hw_delay, hw_delay_complete, 0);